RE: Sending responses with unknown body size in HTTP/2

Hi Amos,

Thanks for the reply!

> Valid yes. Section "MAY send a Content-Length header". So the
> inverse is also logically true, SHOULD not send one - especially in the
> case where length is unknown.

> Senders are not obliged to send Content-Length for HTTP/2, they can
> simply END_STREAM on a DATA frame.

That's what I was thinking, good to hear others interpret the same way.

>> When thinking through this problem a while back, I had thought that in
>> the HTTP/2 case it would be possible to append the content-length as a
>> trailer but I convinced myself that was also invalid due to a number of
>> other HTTP semantic rules.

>Which ones? IMO it is valid, though only useful for the message
> integrity checking.

Well, RFC7230 section 4.1.2 says:

   A sender MUST NOT generate a trailer that contains a field necessary
   for message framing (e.g., Transfer-Encoding and Content-Length),
   routing (e.g., Host), request modifiers (e.g., controls and
   conditionals in Section 5 of [RFC7231]), authentication (e.g., see
   [RFC7235] and [RFC6265]), response control data (e.g., see Section
   7.1 of [RFC7231]), or determining how to process the payload (e.g.,
   Content-Encoding, Content-Type, Content-Range, and Trailer).

I originally had a design where I sent a 206 Partial Reponse. In the leading HEADERS I had a content-length and in the trailing headers I had a content-range and a signature (draft-cavage-http-signatures-09). However, after rereading the above statement and combining it with RFC section 4.1 I came to the conclusion that not only was that design invalid but that the selection of headers that *are* allowed in a trailer is actually quite small. Especially in HTTP/2 where chunked encoding is not permitted.

I'd love to know if my evaluation was incorrect, which would allow me to return to the original design.


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Received on Saturday, 27 January 2018 00:02:03 UTC